1. Technical Field
The present invention relates to a measuring apparatus, a measuring method, a recording medium, and a test apparatus. Particularly, the present invention relates to a measuring apparatus, a measuring method, a recording medium, and a test apparatus for measuring a quadrature modulator.
2. Related Art
A signal output from a quadrature modulator or a quadrature demodulator includes a carrier phase error (also called quadrature error) that occurs between the I signal side and Q signal side of the quadrature modulator or the quadrature demodulator, an amplitude error (also called gain error) that occurs between the I signal side and Q signal side, and an error according to a skew between an I signal and a Q signal. Non-Patent Literature 1 describes a method for measuring these errors in the quadrature modulator. This method supplies a complex sine wave signal to the quadrature modulator, which is the object of measurement, detects a modulated signal output from the quadrature modulator, and displays a Lissajous waveform of the detected signal on an oscilloscope or the like. Then, this method calculates an amplitude error based on the ratio between the longer diameter and shorter diameter of an ellipse of the Lissajous waveform displayed on the oscilloscope or the like, and calculates a carrier phase error based on the angle of the ellipse.    [Non-Patent Literature 1] “TECHNICAL FEATURE”, MICROWAVE JOURNAL, USA, Horizon House Publications INC, January 2000, page 38.
However, since the longer diameter and shorter diameter and the angle of an ellipse have to be calculated, the method described in Non-Patent Literature 1 cannot precisely calculate a carrier phase error and an amplitude error. Further, the quadrature modulator and the quadrature demodulator will produce a greater impact from an error according to a skew, in a case where the signal to be processed is several ten MHz to several hundred MHz or larger. However, the method described in Non-Patent Literature 1 cannot measure a skew.